In the construction industry, it is often necessary to insert pipe-like bodies into the earth. Such pipe like bodies are referred to as caissons in most situations and often as casings in the context of a pipe that is inserted into the earth during drilling operations.
As examples, caissons are inserted into the earth during new construction as part of a foundation for a structure; caissons are also commonly driven under a bridge or the like when providing additional structural resistance to earthquake damage. Casings are employed when drilling a hole to prevent the earth from collapsing into the hole as it is drilled.
In this application, the term "caisson" will be used to refer to any pipe like body that is driven into the earth, including the casings used in drilling operations.
To insert a caisson into the earth, a large driving force must be applied thereto. Often, vibratory devices are employed to introduce a vibratory force along the axis of the caisson during the driving process. The combination of a static driving force with a dynamic vibratory force is usually sufficient to overcome the earth's resistance and allow the caisson to be inserted therein.
A clamping assembly must be provided to allow vibratory forces to be effectively transmitted to the caisson. Such clamping assemblies have heretofore normally been adapted to engage the upper end of the caisson. But as described in copending patent application Ser. No. 08/408,023 filed by the present inventor, now the U.S. Pat. No. 5,544,979, clamp assemblies also exist that grip the side of the caisson as it is being driven into the earth.
The present invention relates to clamp assemblies that engage the upper end of the caisson. Normally, such clamp assemblies comprise a cast beam having individual clamps movably mounted on each end thereof. A vibratory device is bolted to an upper surface of the beam. The beam is then arranged above the caisson upper end and lowered such that opposing portions of the caisson upper end are received between gripping members of the clamps. The clamps are then actuated such that the gripping members grip the caisson upper end and thus fix the caisson relative to the vibratory device.
The vibratory device is then operated to create a vibratory force that, in combination with the weight of the vibratory device, clamping assembly, and caisson, drives the caisson into the earth.
This arrangement usually works well with caissons of relatively small diameter. With larger caisson diameters, however, the vibratory forces often cause walls of the caisson to vibrate, or diaphragm, especially under hard soil conditions. This diaphragming of the caisson absorbs the vibratory driving forces, preventing the caisson from being driven into the earth and oftentimes resulting in damage to the caisson. At a minimum, diaphragming requires that the driving process be performed more slowly.
An undesirable side effect of diaphragming of the caisson is that the vibratory forces are transmitted laterally by the caisson walls into the adjacent soil instead of vertically through the caisson to the lower end thereof. In many situations, such as when the caisson is being inserted adjacent to a building or other structure, these laterally transmitted vibratory forces are highly undesirable because they might unduly stress the adjacent structure.
The most common method of overcoming the problem of diaphragming is simply to increase the wall thickness of the caisson. The thicker caisson wall results in a more rigid caisson that resists diaphragming and can therefore be more easily driven into the earth.
Caissons with thicker walls are significantly more expensive, however, and the need exists for apparatus and methods for driving caisson assemblies into the earth that allow the use of thin walled caissons under more circumstances.